This invention relates to semiconductor devices generally, and more particularly, to a semiconductor structure having environmentally isolated circuit elements disposed thereon.
Integrated circuit devices generally comprise one or more circuit elements, such as P-N junction devices, MOS devices (diodes, transistors, etc.) and resistors, capacitors, and the like formed on or within a substrate. These devices, in particular, have found a multitude of applications in the field of electronics, ranging from rectification of electrical currents to amplification of electrical signals and many others. Such devices have also been used in the conversion of a mechanical or acoustical signal into an electrical signal, or vice versa.
Although semiconductor devices are extremely small, they possess high reliability and have been utilized in many applications where the external environment imposes difficult operating conditions on the semiconductor structure. For example, semiconductor transducers have been employed in aircraft, automobiles, and other vehicles in which the transducer is exposed to moisture, fuel, solvents, hydraulics, and the elements in general. Exposure to moisture and to airborne contaminants prevalent in the aforementioned environments can harm the piezoresistive elements employed in conventional transducers. Integrated circuit chips may also be exposed to the same environmental conditions and p-n junction devices utilized thereon are equally susceptible to damage from such operating conditions. However, it is well known that any of these devices should be enclosed in some sort of hermetic package for environmental protection.
Accordingly, many schemes have been devised for the protection of the circuit elements of integrated circuit chips and other semiconductor structures in harsh environmental conditions, but these are uneconomical, imperfect, and introduce various problems. One widely accepted method of providing protection to the piezoresistive elements of semiconductor pressure transducer, for example, is to utilize a metal isolation diaphragm coupling the pressure applied through a fluid transmitting medium. For one example of a device constructed in accordance with this approach, see U.S. Pat. No. 4,406,993 entitled OIL FILLED PRESSURE TRANSDUCERS, issued on Sep. 27, 1983 to Anthony D. Kurtz and assigned to the assignee herein. One problem associated with fluid encased configurations, however, is that the oil must be seated in an absolutely hermetic manner. Such a seal is difficult to obtain with a silicon chip. Another disadvantage is that the trapped oil expands at high temperatures, thereby causing an unwanted pressure signal. Accordingly, devices constructed in that manner are not suitable for the hot sections of aeronautical propulsion systems and other applications in which high temperature conditions exist.
In U.S. Pat. No. 3,900,811 entitled ECONOMICAL PRESSURE TRANSDUCER ASSEMBLIES, METHODS OF FABRICATING AND MOUNTING THE SAME, issued on Aug. 19, 1975 to Anthony D. Kurtz and assigned to the assignee herein, there is disclosed another technique for hermetically isolating a pressure transducer assembly in which the transducer chip is placed in a transistor housing assembly such as a TO-5 package. This is accommodated by ball bonding the contacts of the transducer to the posts of a Kovar base plate and capping it with a cylindrical Kovar header. A chief disadvantage of this technique, however, is that it requires the individual steps of ball bonding and hermetic packaging, which can not be performed as part of a batch process. There are of course a multitude of other hermetic headers or flat pack enclosures for assuring environmental protection. However, all involved separately mounting chips or dies within each enclosure, making individual electrical contacts from selected points on the chip or die to terminal pads on the enclosures and then individually sealing each enclosure.
It is therefore an object of the present invention to provide an environmentally isolated semiconductor structure which prevents contamination of the semiconductor elements disposed thereon. This invention seeks to provide a mechanical structure which is practical and economical for implementation in hermetically sealing the circuit elements disposed on or in any integrated circuit chip, thereby protecting such elements from environmental contamination. This sealing process is accomplished in wafer form so that a multiplicity of enclosures and lead connections are simultaneously made in a batch process.